Electrolysis and redox
5 marks · HardThe apparatus below is used to electrolyse molten tin(II) chloride (SnCl₂). Tin(II) ions (Sn²⁺) and chloride ions (Cl⁻) move towards the electrodes and react.
(a) State what is meant by 'discharging' a tin(II) ion during the electrolysis of molten tin(II) chloride.
State what is meant by 'discharging' a tin(II) ion during the electrolysis of molten tin(II) chloride.
Explain, in terms of electron transfer, what happens to a tin(II) ion at the cathode in this process.
Write a half-equation for the reaction involving tin(II) ions at the cathode.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Discharging a tin(II) ion means it loses its electric charge by gaining electrons to form a neutral tin atom.
(b) At the cathode, a tin(II) ion (Sn²⁺) gains two electrons (is reduced) to become a tin atom. This is reduction by electron gain.
(c) \ce{Sn^{2+} + 2e^- -> Sn} · must show Correct ionic symbols and electron transfer
Common mistakes: Mixing up cathode/anode reactions; Incorrect half-equation balancing
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly explains that discharging means loss of charge (tin(II) ion becomes a neutral atom).
B2 (a) · 1 mark · Refers to gain of electrons by the tin(II) ion on discharge.
M1 (b) · 1 mark · States that Sn²⁺ gains electrons at the cathode.
A1 (b) · 1 mark · States or implies 2 electrons are gained; mentions reduction or becoming neutral atom.
B3 (c) · 1 mark · Correct half-equation: \ce{Sn^{2+} + 2e^- -> Sn}
Worked solution
a) Discharging a tin(II) ion means that it loses its electric charge by gaining electrons and forms a neutral tin atom.
b) At the cathode, each tin(II) ion gains two electrons from the electrode. This added electron transfer changes the ion (Sn²⁺) into a tin atom (Sn). This is reduction because the ion gains electrons.